Net shape manufacturing using carbon nanotubes

ABSTRACT

The present invention provides methods and systems for net shaped manufacturing using carbon nanotubes. Generally, an automatic control unit is used to place reaction units in the proper location to produce a component part of carbon nanotubes in a predetermined configuration. The reaction units include a carbon vaporization unit, a carbon feed/injection unit and a gas pressure/temperature control isolation unit. The carbon feed/injection unit advantageously operates to inject carbon based materials (e.g., graphite powder, solid graphite or carbon based gas) into an reaction area at a predetermined rate in which the carbon vaporization unit provides energy capable of dissociating carbon atoms from the injected carbon based material to produce a predetermined concentration of carbon vapor within the reaction area. The gas pressure/temperature control isolation unit operates to control the pressure and temperature of the reaction area to promote the growth of carbon nanotubes.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field of the Invention

[0002] This invention relates to manufacturing carbon based materialsand, more particularly, to a method and system for net shapemanufacturing using carbon nanotubes.

[0003] 2. Background of the Invention

[0004] In addition to the more common allotropes of carbon, namelydiamond and graphite, there exist a third form which forms a network ofstructures called fallerenes. The best known, discovered in 1985, iscalled the Buckyball or to give its technical name Buck minsterfullerene. ABuckyball structure is a pure carbon molecule comprisingexactly sixty carbon atoms. Generally, each carbon atom is bonded tothree other carbon atoms in the form of a spherical structure. Recentresearch has identified another type of fallerene which appears as ahollow tubular structure known as the nanotube. The carbon nanotubeappears as an elongated fiber and yet it is hollow and inherits theperfection of atomic arrangements made famous by its predecessor theBuckyball. Carbon nanotubes consist of two dimensional hexagonal sheetsfolded together and capped at both ends by a fullerene cap. There lengthcan be millions of times greater than their small diameter. Thus, carbonnanotubes are effectively Buckyball structures extended out as longstrands rather than spheres.

[0005] Development of carbon molecular growth began with the manufactureof carbon fibers and, while these conventional carbon fibers are readilymade very long, the graphite sheets within the carbon fibers are eithernot closed tubes or do not extend continuously along the length of thefiber. The result is sharply decreased tensile strength, electricalconductivity and chemical resistance compared to a carbon nanotube.Thus, development of fullerenes, such as carbon nanotubes, has continuedin an effort to develop materials with improved physical properties.

[0006] Carbon nanotubes exhibit mechanical, electronic and magneticproperties which are in tuneable by varying the diameter, number ofconcentric shelves and orientation of the fibers. Practical carbonnanotube based materials require eliminating defects and other reactionproducts, maximizing the nanotube yield, and synthetically controllingthe tube length and orientation. Currently there exist three primarymethods for producing carbon nanotubes. These methods include, forexample, Electric Arc Discharge, Resistive Heating and Laser Ablation.

[0007] The Electric Arc Discharge process works by utilizing two carbon(graphite) electrodes in an arc welding type process. The welder isturned on and the rod ends are held against each other in an argonatmosphere to produce or grow carbon nanotubes. The yield rate of carbonnanotubes of this process is extremely low and the growth of the carbonnanotube orientation are random in nature delivering only undefinedconfigurations of growth material.

[0008] In Resistive Heating type processes, the flllerenes are formedwhen a carbon rod or carbon containing gas is dissociated by resistiveheating under a controlled atmosphere. A resisted heating of the rodcauses the rod to emit a faint gray white plum soot like materialcomprising fullerenes. The fallerenes collect on glass shields thatsurround the carbon rod and must be separated from non-desirablecomponents in a subsequent process. Again, the yield rate ofthe carbonnanotubes is extremely low and orientation is random delivering onlyundefined configurations of growth material.

[0009] The Laser Ablation batch type process works by ablating agraphite target containing a small metal particle concentration with apulsed laser while providing a temperature controlled space for thecarbon atoms and carbon vapor to combine to grow a fullerene structuresuch as a nanotube. The fallerene structure falls out in a type ofcarbon soot. The desired fullerene structure is subsequently extractedfrom the soot by an acid reflux cleaning system. Although the LaserAblation process has experienced an improved yield rate, relative to theabove-mentioned processes, this batch type process approach isuneconomical for use in industrial application because there currentlyexist no method for controlling the orientation and shaping of thecarbon nanotubes. None of the above-mentioned batch methods are used todelivered large-scale production of carbon nanotubes or crystalline typecarbon nanotubes with a defined orientation in a net shape typemanufacturing arrangement.

[0010] The above-mnentioned and other disadvantages of the prior art areovercome by the present invention, for example, by providing a methodand system for net shape manufacturing using carbon nanotubes.

SUMMARY OF THE INVENTION

[0011] The present invention achieves technical advantages as a methodand system for net shaped manufacturing using carbon nanotubes. Anautomatic control unit is used to place reaction units in the properlocation to produce a component part of carbon nanotubes in apredetermined shape. The reaction units include a carbon vaporizationunit, a carbon and catalyst feed/injection unit and a gaspressure/temperature control isolation unit. The carbon/catalystfeed/injection unit advantageously operates to inject carbon basedmaterials (e.g., graphite powder, solid graphite or carbon based gas)into an reaction area at a predetermined rate in which the carbonvaporization unit provides energy capable of dissociating carbon atomsfrom the injected carbon based material to produce a predeterminedconcentration of carbon vapor within the reaction area. The gaspressure/temperature control isolation unit operates to control thepressure and temperature of the reaction area to promote the growth ofcarbon nanotubes.

[0012] Among the new advantages of the present invention are: First,preferentially oriented carbon nanotubes can more economically befabricated into component parts; And, since preferentially orientedcarbon nanotubes exhibit both superior strength and electricalconductivity, stronger structural materials can be fabricated into acomponent which utilizes both structural advantages and electronicapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a more complete understanding of the present invention,reference is made to the following detailed description taken inconjunction with the accompanying drawings wherein:

[0014]FIG. 1 illustrates a flowchart of a method for net shapemanufacturing using carbon nanotubes in accordance with the presentinvention;

[0015]FIG. 2 illustrates one embodiment of a system architectureembodying the present invention; and

[0016]FIG. 3. is an exemplary illustration of a synthesis head which canbe used to implement the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The numerous innovative teachings of the present application willbe described with particular reference to the presently preferredexemplary embodiments. However, it should be understood that this classof embodiments provides only a few examples of the many advantageoususes of innovative teachings herein. In general, statements made in thespecification of the present application do not necessarily delimit anyof the various claimed inventions. Moreover, some statements may applyto some inventive features but not to others.

[0018] Referring now to the Drawings, and more particularly, to FIG. 1,there is illustrated a method of manufacturing using carbon nanotubes inaccordance with the present invention, The process begins with aninjection step 122. In the injection step 122, carbon based material isinjected into a reaction area for further operations to be performed.The reaction area is the area in which carbon nanotubes nucleate orgrow. The carbon based material is the feed stock for carbon atomsnecessary for the nucleation of carbon nanotubes. In a preferredembodiment, the carbon based material is a pure carbon molecule.However, the feed stock can be a combination of carbon and other typesof material. The carbon based material can be, for example, apowder,solid or gaseous form (such as graphite powder, solid carbon rod orcarbon gas).

[0019] Next, in a dissociation step 124, carbon atoms are dissociated orvaporized from the carbon based feed stock which is injected into thereaction area. Dissociation is attained by heating the carbon based feedstock to a temperature sufficient to form a carbon vapor. Thetemperature will depend on the type of carbon based feed stock used,however, temperatures can range from 800° C. to 3000° C. Thesetemperatures can be attained through the use of, for example, electricarc discharge electrodes, resistive heating elements, laser, electronbeam or other heating type processes.

[0020] In an isolating step 126, the reaction area is maintained under acontrolled pressure and temperature profile. The controlled pressure isused to control the location of the dissociated carbon atoms at anoptimum distance from the nucleating carbon nanotubes. The absolutepressure of the atmosphere selected to form carbon nanotubes can be aminimum of 0.001 Torr and can range up to a maximum of 20,000 Torr.Lower pressures produce carbon vapors having a lower carbonconcentration, which allows production of carbon nanotubes withpredetermined orientations. Smaller diameter carbon nanotubes can beattained at higher pressures. Also, although the dissociated carbonvapor will initially reside at very high temperatures, the carbon vaporneeds to be cooled at a controlled rate to reach an energy state toallow the vapor to form into a predetermined solid nanotube structure.In the isolating step 126, the pressure controlled area can betemperature controlled to allow a gradual cooling from the initialtemperature needed to dissociated the carbon atoms.

[0021] Finally, in a controlling step 128, the above-mentioned reactioncomponents (i.e., injection step 122, dissociation step 124 andisolating step 126) are precisely and accurately placed in a locationpredetermined by the configuration of a component part to be fabricated.A component part is fabricated by stacking multiple cross-sectionallayers of carbon nanotubes until the component part is completed in apredetermined physical shape. Thus, this control type system is basedupon material additive layer manufacturing. The process can be computeraided by first decomposing the predetermined shape into very thincross-sectional layers and subsequently placing the reaction componentsin the proper locations to fabricate each cross-sectional layer fromcarbon nanotubes. Subsequent cross-sectional layers are stacked on theprevious cross-sectional layer. The growth of previously depositedcarbon nanotubes can be continued with each subsequent cross-sectionallayer.

[0022] In another embodiment, to control nucleation of carbon nanotubeswith a predetermined physical properties, a catalyst or metal compoundor material can be combined with the carbon based feed stock. The carbonbased feed stock and the metal material, when used, is combined prior todissociation step 124. The combination can be made, for example, bymixing graphite with the metal material and then processing therelatively homogenous mixture into a rod in accordance with methodsknown in the art. The rod containing the combination carbon and metalmaterial is then utilized in the dissociation step 124 described herein.However, a carbon based feed stock and a metal based feed stock can bedissociated in separate steps and subsequently placed in the reactionarea. Additionally, the type and concentration of metal material can bevaried during the fabrication process of the component part to allowfurther variance of the physical properties of the carbon nanotubes.

[0023] For example, the process works by injecting methane gas into thereaction area and dissociating the methane gas into ionized hydrogen andcarbon atoms. When this is done in the presence of a metallic particlethe ionized carbon atoms cover the surface area of the metallicparticle. When the carbon atoms on the metallic particle come in contactwith each other, they form covalent bonds in the most energeticallystable formation. By choosing a metallic particle of the predeterminedshape and size, carbon nanotubes form with defined diameters andphysical properties. As a carbon nanotube is formed and it separatesfrom the metallic particle, the carbon on the surface area of themetallic particle is replaced with more ionized carbon. Thus, thereaction can continue indefinitely until one of the following occurs: 1)the carbon feed stock is withheld from the reaction area; 2) thereaction isolation conditions are changed so that the formation ofcarbon nanotubes is no longer favorable; or 3) the concentrationofmetallic particles are increased to allow the metallic particles tocome in contact with each other and grow to a size or shape that doesnot allow further growth of the carbon nanotubes. Also, In situdiagnostics can be used to evaluate the carbon nanotube growth process.Thus, the nucleation of the carbon nanotubes can be varied to allowcustom tailoring of the physical properties in real time. In situdiagnostics is the process of evaluating chemical reactions as theyoccur to determine their exact conditions in terms of their energy,chemical reactants, growth orientation, etc.

[0024] Now referring to FIG. 2, there is illustrated a system 200 fornet shape manufacturing using carbon nanotubes in accordance with thepresent invention. The system 200 comprises an automatic control unit210 and reaction units which includes a carbon feed/injection unit 230,a carbon dissociation unit 220 and a gas pressure/temperature controlisolation unit 240.

[0025] The carbon feed/injection unit 230 is used to inject a carbonbased material into a predetermined area for further operations to beperformed. The arbon based material is the feed stock for carbon atomsnecessary for the nucleation ofcarbon nanotubes. The injection rate iscontrolled by and through communication with the automatic control unit210. In a preferred embodiment, the carbon based material is a purecarbon molecule. However, the feed stock can be a combination of carbonand other types of material. The carbon based material can be, forexample, a powder, solid or gaseous form (e.g., graphite powder, solidcarbon rod or carbon gas). The carbon feed/injection unit 230 can beequipped with a type of hopper which allows the continuous injection offeed stock without requiring the manufacturing system to slow or pausefor the reloading of feed stock.

[0026] The carbon dissociation unit 220 dissociates carbon atoms fromthe feed stock which is injected into the predetermined area.Dissociation is attained by heating the carbon based feed stock to atemperature sufficient to form a carbon vapor. The carbon dissociationunit 220 is capable of providing enough energy to vaporizing the feedstock into carbon molecules. The carbon dissociation unit 220 cancomprise, for example, electric arc discharge electrodes, resistiveheating elements, laser, electron beam or other heating type process.Energy level output, of the carbon dissociation unit 220, is controlledand varied by and through communication with the automatic control unit210.

[0027] The gas pressure/temperature control isolation unit 240 iscapable of varying the pressure and temperature of an predeterminedarea. Varying the pressure is effectuated by evacuating or pumping agas, preferably an inert gas, into the predetermined area. Inert gasesinclude, for example, helium, argon and xenon. Other gases, which arenot reactive with the vaporized carbon can be used. The pressure can bevaried from about 0.001 Torr to 20,000 Torr. Pressure and temperature,of the gas pressure/temperature control unit 240, is controlled andvaried through communication with the automatic control unit 210.

[0028] Although the dissociated carbon vapor will initially reside atvery high temperatures, the carbon vapor needs to be cooled at acontrolled rate to reach an energy state to allow the vapor to form intoa predetermined solid nanotube structure. The gas pressure/temperaturecontrol unit 240 comprises a heating device (not shown) to heat thepressure controlled area at temperatures which allow a gradual coolingfrom the initial temperature needed to dissociated the carbon atoms.

[0029] Finally, the automatic control unit 210 precisely and accuratelyplaces the above-mentioned reaction units 220, 230, 240 in apredetermined area to nucleate carbon nanotubes into the configurationof a component part. The component part is fabricated by stackingmultiple cross-sectional layers of carbon nanotubes until the componentpart is completed in apredetermined physical shape. The automaticcontrol unit 210 can be computer aided to allow the configuration of thecomponent part to be decomposed into very thin cross-sectional layers.Subsequently, the automatic control unit 210 places the reaction units220, 230, 240 in apattern of reaction areas determined by the decomposedcross-sectional layers. Carbon nanotubes are nucleated in the multiplereaction areas to form the shape of each cross-sectional layer pattern.Each subsequent cross-section is stacked upon the previouscross-sectional layer. Thus, the component part is fabricated bymultiple stacked cross-sectional layers of nucleated carbon nanotubes.Growth of previously deposited carbon nanotubes can be continued withthe stacking of each subsequent cross sectional layer and additionallayers of newly nucleated carbon nanotubes can also be added.

[0030] In another embodiment, the net shape manufacturing system 200 caninclude a substrate (not shown) to support the nucleating carbonnanotubes. Layers of sacrificial substrates can also be simultaneouslybuilt up to support more complex comiponent part configurations. Thesubstrate can be embedded with seed particles to assist the growth ofthe nanotubes. The seed particles, such as carbon nanotubes or selectedmetal particles, are arranged in a pattern consistent with thepredetermined configuration of the component part to be fabricated.

[0031] The strength of the component part can be improved by definingthe orientation of the nucleating nanotubes. When large bundles ofcarbon nanotubes grow together, they eventually form amacroscopiccrystal. However, this type of crystal is not expected to have good bulkmechanical strength when compared to single carbon nanotubes. The bondsthat hold the individual carbon nanotubes together in the bundles areweek Van der Waals bonds. Essentially, these lateral bonds form slipplanes in which bulk material failure could occur. The automatic controlunit 210 is capable of placing and controlling the reaction units 220,230, 240 to nucleated helical growth of short length carbon nanotubessuch that each successive layer of the helix blocks the slip plane ofthe previous layer. In addition to the helical growth technique, thegrowth direction vector of the crystal can be changed (either allowed tohappen randomly or in a controlled manner) such that dislocation betweenindividual carbon nanotubes are not allowed to propagate through out thecrystal. In either the random or controlled manner, the growthproperties are maintained to ensure uniform mechanical and electricalproperties. Thus, the problems encountered with slip planes can bereduced or eliminated by using the above-described net shapemanufacturing system to control the carbon nanotube growth in acomponent part. Additionally, the automatic control unit 210 can use insitu diagnostics to evaluate the carbon nanotube growth in real time andadjust during processing to control and vary the physical properties ofthe carbon nanotubes.

[0032] Now referring to FIG. 3, there is illustrated a synthesis head300 which can be used in net shape manufacture using carbon nanotubes inaccordance with the present inventor A control arm 310 is coupled to thereaction units 220, 230, 240. The control aim 310 can be, for example, a5 or 6 axis rotating type arm. The movement of the control arm 310 iscontrolled by the automatic control unit 210 (FIG. 2) through a wirelineor wireless type connection. The automatic control unit 210 instructsthe control arm to place the reaction units 220, 230, 240 such thatcarbon nanotube nucleation is effectuated in the reaction area 320.Thus, the reaction area 320 can be continuously maneuvered in thepattern determined by the decomposed cross-sectional layers.

[0033] Preferentially grown carbon nanotubes add tremendous capabilityand functionality to materials and systems. For example, carbonnanotubes for use as structural materials show strength to weight ratiosof up to 126 to 1 over titanium and 142 to 1 over aluminum. Economicanalysis indicates that this weight savings translates into largeproduction cost reductions depending on the production rate. Along withuse as a structural material, carbon nanotubes have many otherattributes that increase the capabilities ofmaterials and systems.

[0034] Additionally, the carbon atomic bonds of carbon nanotubes can bearranged in a multitude of ways giving the nucleated carbon nanotubesconductivities ranging from an insulator to a semiconductor to ametallic conductor. This range of conductivity is due to the helicalsymmetry or chirality of the nanotubes. Thus, the present invention canbe used to integrate both structural and electronic advantageouscharacteristics at the same time or within the same component part. Asthe cross-sectional layers are added, physical properties can be variedby individual control of the reaction units 220, 230, 240. By customtailoring physical properties of individual or groups of carbonnanotubes, multi-functionality can be achieved for applications such aselectronics, electrical routing, piezoelectric and power storagesystems. Thus, physical structures, such as aerospace wing structures,can be produced with embedded electronics type circuits. Assumingconventional manufacturing methods could be used to fabricate these typeproducts, such methods would in all probability require additional timeconsuming operations, including the need for custom fixturing andtooling, high strength material joining processes, and complex assemblyoperations.

[0035] Although a preferred embodiment of the method and system of thepresent invention has been illustrated in the accompanied drawings anddescribed in the foregoing detailed description, it is understood thatthe invention is not limited to the embodiment disclosed, but is capableof numerous rearrangements, modifications, and substitutions withoutdeparting from the spirit of the invention as set forth and defined bythe following claims.

What is claimed is:
 1. A method of manufacturing a component part havinga predetermined configuration using carbon nanotubes, comprising thesteps of: injecting carbon based material into a reaction area at apredetermined rate; dissociating carbon atoms from said carbon basedmaterial at a predetermined rate; isolating the reaction area at apredetermined temperature and a predetermined pressure, wherein saidcarbon nanotubes nucleate in said reaction area; and dynamicallylocating said injecting, dissociating and isolating steps to nucleatesaid carbon nanotubes in said predetermined configuration.
 2. The methodof claim 1 further comprising the steps of: decomposing saidpredetermined configuration into multiple cross-sectional layers; andrepeating said step of dynamically locating said injecting, dissociatingand isolating steps for each said multiple cross-sectional layer,wherein each successive cross-sectional layer is stacked on a previouscross-sectional layer.
 3. The method of claim 1 further comprising thestep of dynamically varying a rate of injection of said carbon basedmaterial.
 4. The method of claim 1 further comprising the step ofdynamically varying a rate of dissociation from said carbon basedmaterial.
 5. The method of claim 1 further comprising the stepdynamically varying said predetermined pressure and predeterminedtemperature.
 6. The method of claim 1, wherein the step of dissociatingis effectuated by a laser, an electron beam, or an electrical arcdischarge unit.
 7. The method of claim 1, wherein said carbon basedmaterial further comprises a metal based material.
 8. The method ofclaim 7, further comprising the step of dynamically varying aconcentration of said metal based material.
 9. The method of claim Ifurther comprising the steps of: injecting a carbon based materialhaving a first metal based material; and injecting a second carbon basedmaterial having a second metal based material.
 10. The method of claim1, further comprising the step of adjusting a growth direction of saidcarbon nanotube during a growth period.
 11. A system of manufacturing acomponent part having a predetermined configuration using carbonnanotubes, comprising: carbon injection unit, said carbon injection unitinjecting a carbon based material into a reaction area; carbondissociation unit, said carbon dissociation unit dissociating carbonfrom said carbon based material; isolation unit, said isolation unitcontrolling the pressure and temperature of said reaction area, whereinsaid carbon nanotubes nucleate within said reaction area; and controlunit in communication with and capable of dynamically locating saidcarbon injection unit, carbon dissociation unit and isolation unit in apredetermined pattern to nucleate said carbon nanotubes in saidpredetermined configuration.
 12. The system of claim 11, wherein saidcontrol unit further decomposing said predetermined configuration intomultiple cross-sectional layers, wherein nucleation of said carbonnanotubes is repeated for each said multiple cross-sectional layer, andwherein each successive layer of carbon nanotubes is stacked on aprevious layer.
 13. The system of claim 11, wherein said control unitfurther dynamically varies carbon based material injection rate.
 14. Thesystem of claim 13, wherein said control unit further dynamically variesdissociation rate.
 15. The system of claim 11, wherein said control unitfurther dynamically varies said pressure and temperature of saidreaction area.
 16. The system of claim 11, wherein said carbondissociation unit comprises a laser, an electron beam and an electricalarc discharge unit.
 17. The system of claim 11, wherein said carbonbased material further includes at least one type of metal basedmaterial.
 18. The system of claim 17, wherein said control unit furtherdynamically varies an amount and type of metal based material withinsaid carbon based material.
 19. The system of claim 12 further includinga substrate capable of providing an initial nucleation surface for saidcarbon nanotubes.
 20. The system of claim 19, wherein said substrateincludes seed material arranged in a predetermined pattern consistentwith a first cross-sectional layer of said multiple cross-sectionallayers.